A good summary but I would suggest you left out one of his biggest failures, Ireland.
Following the 1798 rebellion there was perhaps the greatest chance in history for Great Britain and Ireland to be reconciled for a fresh start and to allow Ireland to become a happy partner in the British Union in the same way that Scotland had become.
The disaster of 1798 in the middle of the Napoleonic war showed how shockingly badly Ireland was being governed. A small cabal of reactionary protestant bigots in Dublin controlled with an iron fist a desperately poor and oppressed majority-Catholic Irish population (no I am not a whingeing Irishman with a chip on my shoulder, these are simple historical facts). It was a time for London to march in and clean house and it almost did so.
Pushing through the Act of Union was achieved through bribing the Irish House of Commons (as well as being bigoted know-nothings they were also extremely corrupt) and at this point Ireland could have been admitted to the newly created United Kingdom as a sister nation with dignity and equality.
The Irish Catholic church was completely behind the Union as they recognised they could get a fairer deal from London than the bigoted minority in Dublin (it is one of the great ironies of history that the Catholic church supported Union while the Orange Order, the now loudest proclaimers of their Unionist loyalty, opposed it). Irish Liberals (in the old proper sense of the word) of all stripes also recognised the time for change had come, and even some of the protestant gentry, scared sh!tless by how close they had come to being massacred in the rebellion came around to Union, it was the last golden opportunity to put right the terrible wrongs that Ireland had suffered under British rule and start again with a clean slate.
George III blew it.
A simple, literal-minded man, with much sympathy with the backwoodsmen of the Irish ruling class rather than the sensible advice of William Pitt, he could not accept the right of Catholics to be elected to the House of Commons, thereby disenfranchising the vast majority of the Irish people. Ireland came into the Union as a second-class partner, her wrongs were not to righted, her people would not be equal, the resentment against British rule would bubble and simmer on after all.
The Act of Union failed, it failed because of George III. And I suggest that was a much greater failure than losing the American colonies, which was after all ultimately to Britain’s great benefit.
You’re quite correct - for various reasons, I don’t feel able to discuss the Irish issues in detail - I was taught a very warped version of history myself when it came to Ireland and I know it.
But the question was largely about how George III is perceived in Britain and while I agree that his actions towards Ireland should be regarded as a failure, I don’t think they have much impact on how he is perceived in modern Britain as a whole. England - and then Britain - failed time and time again to properly address the issues of Ireland and when modern Britons see the failures at all, they all tend to roll together in their minds.
The trouble is, he took his coronation oath to preserve and uphold the Protestant church very seriously, and be viewed catholic emancipation as a violation of that oath. It would have been wiser to grant it in 1801 but what a lot of Americans don’t understand about George III is that he wasn’t some arbitrary tyrant, he was a man of principle (he was a virgin until he married and never took a mistress unlike most powerful and influential men of the day) and he took what he saw as his constitutional duty very seriously. He was also a very kind and compassionate man who once stopped a job tearing to pieces an insane woman who had tried to stab him, saying ‘leave’ her alone, she is mad, poor thing!’ and she ended up in an asylum instead of being gruesomely executed.